Basic auth / SSL client certificate: dual-method authentication in lighttpd

Software authentication, lighttpd, lua, security, SSL

On my server I’m running several webapps (such as Tiny Tiny RSS, CGP, and Shaarli). They are all running on a private, separate subdomain. As I’m the only user, this subdomain is protected at the server-level with HTTP Basic authentication, and each app is configured to allow full access without requiring any other login.

This works great, is really simple, and has the advantage of being compatible with almost everything (including with the TT-RSS Android client). But basic auth is still a little annoying in modern browsers: there’s an ugly popup, and typing a very long password several times a day isn’t fun. Especially on mobile browsers. So I thought about it, and figured that a nice solution would be to use SSL client certificates to authenticate myself, with a fallback to standard basic auth when using a browser that doesn’t have the certificate or for legacy applications (such as the TT-RSS Android client).

But of course such a setup is not supported by lighttpd, the HTTP server I’m using: SSL client certificates are handled by the mod_ssl module, authentication by the mod_auth module, and they are completely independent, with no way to enable mod_auth if the connection wasn’t authenticated with a client certificate.

However basic auth is a really simplistic process, so writing a module that will perform such an authentication is quite easy: it’s just a matter of writing some Lua code and enabling it with mod_magnet.

So here it is: comfy-auth.lua, a nice a comfy authentication method for lighttpd 😃

(This script depends on two Lua packages: mimetypes and md5, which can easily be installed with luarocks).

I described the configuration I use for SSL client certificates verification yesterday; here’s what’s needed to add support for comfy auth:

The htdigest file is generated with this simple shell script:

# Usage: ./ my_username "My private domain" hunter2 >> /etc/lighttpd/htdigest
hash=`echo -n "$user:$realm:$pass" | md5sum | cut -b -32`
echo "$user:$realm:$hash"

Using this config, I can now authenticate on my private domain using either a client certificate, or simple basic authentication. And it was fun to do 😃


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